Executives at a California chip maker, Applied Materials, highlighted a number of advantages in announcing a merger recently with a smaller Japanese rival, but an important one was barely mentioned: lower taxes.

The merged company will save millions of dollars a year by moving — not to one side of the Pacific or the other, but by reincorporating in the Netherlands.

From New York to Silicon Valley, more and more large American corporations are reducing their tax bill by buying a foreign company and effectively renouncing their United States citizenship.

"It's almost like the holy grail," said Andrew M. Short, a partner in the tax department of Paul Hastings, which advises a number of American corporations on deals. "We spend all of our time working for multinationals, thinking about how we're going to expand their business internationally and keep the taxation of those activities offshore," he added.

Reincorporating in low-tax havens like Bermuda, the Cayman Islands or Ireland — known as "inversions" — has been going on for decades. But as regulation has made the process more onerous over the years, companies can no longer simply open a new office abroad or move to a country where they already do substantial business.

Instead, most inversions today are achieved through multibillion-dollar cross-border mergers and acquisitions. Robert Willens, a corporate tax adviser, estimates there have been about 50 inversions over all. Of those, 20 occurred in the last year and a half, and most of those were done through mergers.

When Applied Materials announced its deal for Tokyo Electron, it said that its effective tax rate would drop to 17 percent from 22 percent as a result. For a company that had nearly $2 billion in profit in 2011, that amounts to savings of about $100 million a year.

Last year, the Eaton Corporation, a power management company from Cleveland, acquired Cooper Industries, based in Ireland, for $13 billion, and reincorporated there. The company expects to save $160 million a year as a result of the move.

In July, Omnicom, the large New York advertising group, agreed to merge with Publicis Groupe, its French rival, in a $35 billion deal. The new company will be based in the Netherlands, resulting in savings of about $80 million a year.

Also in July, Perrigo, a pharmaceutical company from Allegan, Mich., said it would acquire Elan, an Irish drug company, for $6.7 billion. Perrigo will also reincorporate in Ireland, bringing its effective tax rate to 17 percent from 30 percent, and saving the company an estimated $150 million a year, much of it in taxes.

Ireland's 12.5 percent corporate tax rate is a big draw for some companies. Earlier in the year, Actavis, based in Parsippany, N.J., bought Warner Chilcott, a drug maker with headquarters in Dublin, and said it would reincorporate in Ireland, leading to an estimated $150 million in savings over two years.

"These companies are doing the math and seeing they can save a couple hundred million dollars by doing this," said Martin A. Sullivan, chief economist at Tax Analysts, a nonprofit group that publishes analysis about global taxes.

But the small fortunes saved by inverted companies amounts to billions in revenue not collected by Washington.

"The impact in any one year may not be material, but the cumulative impact over time adds up," said J. Richard Harvey, professor at the Villanova University School of Law. "Over time, more multinationals may want to expatriate or invert, and we could wake up in 10 or 20 years and it might be a meaningful number."

The first corporate inversion occurred more than 30 years ago, when McDermott, an oil and gas company, moved to Panama in 1982. Twelve years later, Helen of Troy, which makes household goods like blow dryers, reincorporated in Bermuda. Both those inversions got the attention of the Internal Revenue Service, which enacted rules intended to stem the outflow of corporate tax dollars from the United States.

But the regulations were largely ineffectual and did not stop another wave of inversions from taking place in the late 1990s and early 2000s. Tyco went to Bermuda in 1997 to lower its tax bill. A year later, Fruit of the Loom moved to the Cayman Islands. And in 2001, Ingersoll-Rand reincorporated in Bermuda.

The Jobs Creation Act of 2004 included a provision that made it more difficult to invert, stating that companies that did so must have substantial business activity in the country where they reincorporate. Still, companies again found a way. In 2009, Ensco, a Dallas-based oil services company, reincorporated in London.

The Internal Revenue Service tried to clamp down further, saying that "substantial business activity" means a company must have 25 percent of assets, income and employees in the country where it moves its legal domicile, unless other conditions are met.

Now, after these successive rounds of legislation and rule tightening, the only effective way for an American company to invert is by increasing foreign ownership of its stock to more than 20 percent. And the only feasible way to do that is by reincorporating abroad as part of a merger or acquisition.

After the political scrutiny last decade, companies that invert are loath to say they are doing so for tax reasons. When Aon, the giant insurance broker, moved to London from Chicago, it denied that it was doing so for tax purposes. But in filings with the Securities and Exchange Commission, the company highlighted its tax savings.

"You don't want anybody to think you're doing these deals for tax reasons. They don't want a spotlight on it," Mr. Sullivan of Tax Analysts said. "That's like the kiss of death."

Indeed, few mergers are consummated solely to lower a company's tax bill.

"You're not going to do a merger just to get the company offshore," said Stephen E. Shay, professor at Harvard Law School. "This should be an opportunistic benefit on top of a strategic rationale."

Many companies that have recently moved their domicile for tax reasons have chosen European countries with low tax rates, like Ireland and the Netherlands, rather than be tarred by relocating to Bermuda or a Caribbean tax haven.

In moving to Europe, companies are looking to avoid the scrutiny brought on by moving to such obvious tax shelters, and take advantage of the more favorable business conditions in countries like Ireland, which also has a highly skilled work force.

Once inverted, companies save money through three main techniques. First, they do not have to pay the United States statutory tax rate of 35 percent on their worldwide earnings. That alone can amount to tens of millions in savings each year.

Many companies already get around this by keeping cash from foreign sales abroad. But inverted companies are free to use this cash without paying the steep repatriation tax faced by American companies.

Finally, multinationals that invert have an easier time achieving "earnings stripping," a tax maneuver in which an American subsidiary is loaded up with debt to offset domestic earnings, lowering the effective tax rate paid on sales in the United States.

The savings can be huge. Mr. Sullivan of Tax Analysts found that four oil services companies that inverted had saved $4 billion in taxes over the course of a decade. One of those companies, Transocean, the owner of the Deepwater Horizon platform that exploded in the Gulf of Mexico, saved $1.9 billion.

There are signs that the Obama administration and Congress may try to tighten the rules again. Both the House Ways and Means Committee and the Senate Finance Committee are working on draft legislation for comprehensive tax reform that is expected to include new rules intended to curtail inversions while also trying to make the United States a more competitive place for multinationals to call home.

"There are real financial benefits, and that creates a motivation for management to look for opportunistic opportunities," Professor Shay said. "It's not going to change until the law changes."